Siamese Colour Genetics Course · Lesson 8 of 8
Take everything from the last seven lessons and put it together. Predicting Siamese kitten colours isn’t guesswork or magic — it’s reading each parent’s genes one locus at a time, then combining them. This capstone walks a real pairing from start to finish, so that before the kittens arrive you already know what’s possible, what’s likely, and — just as importantly — what the numbers can and can’t promise you.
This lesson assumes you’ve worked through Lessons 1–7. If a term below is unfamiliar, follow its link back to the lesson that covers it.
In this lesson
- How to work out each parent’s genotype from its colour and pedigree
- How to combine the genes into a full litter prediction
- A complete worked example, step by step
- The limits of prediction — what ratios really mean
- When test matings help, and how the predictor and good records fit in
Step 1 — read each parent
Start by turning each parent into a genotype, gene by gene. Its colour tells you what it shows; its pedigree and what it has produced tell you what it hides. For each locus, ask:
- Base colour (B locus): seal, chocolate or cinnamon? Does the pedigree show it could carry a lower colour?
- Dilution (D locus): is it dense or dilute? If dense, could it carry dilute?
- Caramel modifier, red/tortie, tabby: is any of these in play? (Dm, orange, agouti.)
You can read what a cat shows straight off the coat. What it carries comes from the pedigree — a chocolate parent means it carries chocolate, a dilute parent means it carries dilute, a produced kitten of a given colour proves the carry. This is exactly why records matter: the more you know about what a cat has produced, the tighter your prediction.
Step 2 — work one gene at a time, then combine
The trick that makes this manageable is to never try to do all the genes at once. Work each locus as its own little cross — the four-box logic from Lesson 1 — get the ratio for that gene, then multiply the independent genes together. Separate simple steps beat one tangled calculation every time.
Step 3 — a full worked example
Let’s pair a seal point carrying chocolate and dilute (genotype B/b, D/d) with a blue point carrying chocolate (a blue is a dilute seal, so B/b, dd). Both are solid, non-red, so we only need to track base colour and dilution.
Base colour (B/b × B/b): the familiar three-to-one — three-quarters carry at least one B (seal-based), one-quarter are b/b (chocolate-based).
Dilution (D/d × dd): the dense parent passes D or d equally; the dilute parent can only pass d. So half the kittens are D/d (dense) and half are dd (dilute).
Now multiply the two independent genes together:
- Seal — seal-based (3/4) × dense (1/2) = 3 in 8
- Blue — seal-based (3/4) × dilute (1/2) = 3 in 8
- Chocolate — chocolate-based (1/4) × dense (1/2) = 1 in 8
- Lilac — chocolate-based (1/4) × dilute (1/2) = 1 in 8
Four possible colours from one pairing, in a roughly 3 seal : 3 blue : 1 chocolate : 1 lilac ratio — and many of the seals and blues will themselves carry chocolate, ready to pass it on. That’s the whole course in a single mating: base colour, carrying, and dilution stacked together and read out as a litter.
The limits of prediction
Here’s the honest part, and it matters. Those ratios are probabilities averaged over many litters, not promises about one. A single litter of four from the pairing above could easily be all seal, or two lilacs and two blues, with no chocolate at all. Every kitten is an independent roll of the dice; the ratios only reveal themselves over many kittens. Predict the range of what’s possible with confidence — but hold the exact numbers for any one litter loosely.
Test matings and DNA — turning “maybe” into “known”
When you need to know whether a cat carries a recessive rather than guess, a test mating to a cat that shows the recessive can answer it: a single kitten of that colour proves the carry. A clean litter increases your confidence but never fully proves a cat is clear — a carrier can produce a run of non-carriers by chance. Where a reliable DNA test exists for the gene in question, it settles the matter outright; it’s worth checking the current picture with the breed’s health advisors before relying on visual guesswork.
Let the tools do the arithmetic
Once you understand the logic, you don’t have to do the sums by hand every time. The Siamese colour-point predictor applies exactly these rules to any pairing: set each parent’s colour and what they carry, and it returns every possible kitten colour with its probability — base colour, dilution, caramel, red, tortie and tabby all handled, sexes included. Understanding why it gives the answer it does is the point of this whole course; the predictor just spares you the pencil and paper.
The predictor is only as good as what you tell it, though — and that comes back to records. Knowing what each cat truly carries, across a whole programme, is what turns a rough prediction into a reliable one. Keeping proper pedigrees and litter records (the job of the record-keeping tool I’m building at perfect-pedigrees.com) is what lets you feed the predictor the right genotypes in the first place.
Key takeaways
- Read each parent gene by gene: colour tells you what it shows, pedigree tells you what it carries.
- Work each locus separately, then multiply the independent genes together.
- The worked pairing gives roughly 3 seal : 3 blue : 1 chocolate : 1 lilac.
- Ratios are averages over many litters — never guarantees for a single one.
- Test matings, DNA where available, and good records turn “maybe” into “known.”
That’s the course. You can now look at a Siamese, read a pedigree, and predict the colours a pairing can produce — the same skill that separates a confident breeding decision from a hopeful one. If it’s been useful, the best next step is to join the breeders’ list below — that’s where the extra tips and bonus lessons land.
